1. Field of the Invention
The present invention is related to a driver circuit for switching switch according to capacitor voltage, and more particularly related to a driver circuit for switching switch according to capacitor voltage which controls the average current by switching switch according to capacitor voltage under a continuous conduction mode (CCM).
2. Description of the Prior Art
FIG. 1 is a circuit diagram showing a conventional integrated light emitted diode (LED) circuit. As shown, the conventional integrated LED circuit PA1 includes a load circuit PA11 and a driver circuit PA12. The load circuit PA11 is a LED circuit, and further includes a voltage source PA111, a full bridge rectifier circuit PA112, a resistor PA113, a diode PA114, a capacitor PA115, at least a LED PA116, an inductor PA117, a first switch PA118, a resistor PA119, a capacitor PA120, and a capacitor PA121.
The full bridge rectifier PA112 is coupled to the voltage source PA111 and coupled to the resistor PA113, the diode PA114, the capacitor PA115, and the LED PA116. The inductor PA117 has one end coupled to the diode PA114 and the drain of the first switch PA118 and another end coupled to the capacitor PA115 and the LED PA116. The resistor PA119 is coupled to the source of the first switch PA118 and also to CS node of the driver circuit PA12. The capacitor PA120 is coupled to the resistor PA113 and also to VCC node of the driver circuit PA12. The capacitor PA121 is coupled to COMP node of the driver circuit PA12. The first switch PA118 is coupled to OUT node of the driver circuit PA12.
As the first switch PA118 is conducted, an average circuit Ia is generated flowing through the LED PA116 and an inductor current Ib is generated flowing through the inductor PA117. In general, operation mode of the load circuit PA11 is decided by on time of the first switch PA118, which may control the increasing and decreasing of the inductor current Ib. The average of the peak value and the valley value of the inductor current Ib is the average current Ia. The above mentioned operation modes include the continuous conduction mode (CCM) and the discontinuous conduction mode (DCM).
However, each of the operation modes has both advantage and disadvantage. Take the CCM mode for example, CCM mode has the advantage of small input and output ripple, small total harmonic distortion (THD) and Electro Magnetic Interference (EMI), and easier to executing filtering task, however, under the restriction of circuit design, the load circuit PA11 in present cannot generate an average current Ia to drive the LED PA116 stably such that the light generated by the LED PA116 would be unstable.
For example, under CCM, because the initial charging current of the inductor PA117 in each cycle might be different, the timing to turn on the first switch PA118 cannot be identified accordingly, and the value of the inductor current Ib can be only detected after the first switch PA118 is conducted. In order to output the average current Ia averagely, the time to turn off the first switch PA118 would be varied. In order to output the average current Ia with the default value, it is the conventional method to record the timing the increasing inductor current Ib reaches the default value of the average current Ia but not to turn off the first switch PA118 immediately, the first switch PA118 would be turned off after the inductor current Ib exceeding the default value of the average current Ia for a while (double the time reaching the default value in general). However, such method can only be applied to the inductor PA117 under linear operation. If the inductor PA117 is under nonlinear operation, charging and discharging curves of the inductor current when the first switch PA118 is turned on or off would be nonlinear (such as the case of quick charge/discharge), such that the adjusted average current cannot be the default value (for example, the present value is 1 A but the adjusted average current under the restriction of nonlinear operation is 0.7 A). Thus, there exists the need to improve the technology in present.